DE19543226C2 - Inverter power source - Google Patents

Description

The invention relates to an inverter power source, which for a wide variety of applications Energy conversion can be used (US 51 57 592). Examples include power supplies, Battery chargers, electric welding machines. Inverter power sources are preferred used because they are a significant reduction in size and weight of the Main transformers allow, mostly with frequencies above the human hearing range is operated. There are versions with primary full bridge circuit and Half-bridge circuit common; with the half-bridge circuit, only the symmetrical type is used here considered; the more widespread asymmetrical half-bridge is not from the invention affected.

In the primary full-bridge circuit, four electronic switching elements become two Groups arranged. In each group, two of these switches are in series between the plus and connected to the negative pole of a DC voltage provided by known means. Depending on requirements, free-wheeling diodes are provided in parallel to the switches protect against inverse currents. The previously known inverter circuits now lie between the two midpoints of the half bridges the primary winding of the Main transformers optionally in series with a capacitor and / or a choke. This Capacitor prevents DC biasing of the transformer, but can be omitted, if this premagnetization can be prevented by other measures.

In other known arrangements, the so-called resonant circuits, this has Capacitor an essential function as part of a series resonant circuit. With these In most cases, circuits are still a choke or a saturation choke in series to the primary winding of the main transformer. These resonant circuits will be applied to make the switching of the electronic switches almost lossless, because the switch is turned on when it is de-energized or de-energized or both simultaneously (zero voltage switching and zero current switching).  

It is also known for this purpose, relief capacitors in parallel with the Arrange switches that then greatly reduce the turn-off losses when they are switched off. There is usually a rectifier circuit on the secondary side of the transformer either with two rectifiers and central tapping of the transformer or with four rectifiers in Full bridge switching is common. Depending on the application, the inverter power source is behind the Rectifier still a smoothing choke and if necessary a smoothing capacitor available. In the primary half-bridge circuit, there is only one such half-bridge, the opposite pole for the transformer connection forms a capacitive voltage divider, which also taps the DC voltage source can be at half voltage. Here, too, you can optionally Chokes or saturation chokes are available in series with the transformer. In the transformer circuit resonant circuits in a symmetrical half-bridge circuit become the capacitive The center is usually formed by the split resonance capacitor.

The current components of the Power electronics with their associated control circuits are used, such as Example bipolar transistors, MOS-FETs, IGBTs, GTOs etc.

With all the circuit variants mentioned, each primary-side half-bridge should be like this are controlled that they each have a duty cycle of 50% and that the Voltage of a half-bridge center from one voltage pole to the other in swings around a steady course.

When discussing the disadvantages of the prior art, there are different ones To differentiate circuits.

The circuits resonant in the transformer circuit are known to lead to an unfavorable one Utilization of the electronic switch, since this either for a much higher Current or a higher voltage must be designed. That is what the switching losses are  low and the voltage and current edges flatter, resulting in less interference radiation leads. Due to the resonance technique, however, only during a rather short time interval Transfer energy so that there is no optimal situation for the transformer either. The main disadvantage is that the primary side switch and the transformer be badly exploited.

The circuits that are not resonant in the transformer circuit lead to a simple design considerable switching losses both in the switches themselves and in the secondary side Rectifier diodes because the fast switching operations lead to high diode reverse currents to lead. This also results in strong interference radiation in the secondary circuit.

In order to reduce the switch-off losses of the switches, this variant is also used more often Relief capacitors arranged above the electronic switches.

If inverters of this type with primary-side full bridge at idle or with a small load have to be operated, depending on the necessary modulation range on one or both Half bridges additional auxiliary chokes and capacitors necessary, i.e. primary-side auxiliary Vibration loops that ensure idle operation. The problem arises that the primary-side transformer current and the auxiliary currents of these relief networks overlay certain operating points in such a way that those parallel to the switches Relief capacitors no longer swing around and then the electronic switches Short-circuit the charged capacitors. This can be done after just a few cycles thermal overload and destruction of the switches. To prevent that from happening therefore, a choke must be installed in the transformer circuit, which limits the current flow in the Output rectifier is prevented during the time of swinging (see e.g. K.H. Rinne, K. Theml and O. McCarthy, "An Improved Zero-Voltage on Zero-Current Switching Full Bridge Converter ", PCIM Proceedings, June 1995, p. 69). There are versions in which the Choke is in the primary circuit, other known circuits see chokes on the Secondary side in series to the rectifiers before or as in the lecture mentioned both sides of the transformer. Such chokes slow down the current flow in the transformer circuit and enable the undisturbed completion of the swinging of a half bridge, but have the  major disadvantage that a considerable voltage time area for energy transmission is lost goes. To prevent this, the choke is usually designed as a saturation choke. The disadvantage of this, however, is that the choke is far into the magnetization saturation on both sides is very hot and requires special cooling and that the This reduces the overall efficiency of the inverter. An additional problem of Saturation choke also lies in the fact that they have a high value for small load currents should, but could be omitted at full load, since the existing leakage inductances already enough. But the real behavior is just opposite, because that for their function in the lower current range optimized saturation choke stores with increasing current more and more energy and uses too much in the area of the full control of the inverter Voltage time area, which ultimately leads to poor utilization of the main transformer leads, because transformer and choke are in line.

U.S. Patent No. 5,157,592 to Michael M. Walters addresses the same problem Circuit arrangement described in the secondary circuit in series with the two Rectifier diodes each have a saturation choke. The controller can each have a control winding Premagnetization state of these chokes and thus the lockable voltage time area can be set. Using its own active control circuit with transistors and Operational amplifiers are then set the bias of the chokes so that the Swing conditions are met. This solution leads to an additional one Electronics expenditure and requires an additional measuring transformer for the primary current.

So far, there is only one for the inverters with primary-side half-bridge and capacitive center a limited area of application, because this inverter has little possibility of which Primary side to carry out a comprehensive regulation of the output power. The Control of the switching frequency enables a change in power in only one restricted area. In addition, this type of inverter has the same problems with Swing around and with the diode reverse currents like the one described above Full bridge inverter.

The object of the invention is therefore to create an inverter current source, which achieves better component utilization than the known circuits, whereby especially the voltage time area lost by the chokes is reduced at full load, but the soft current curves of the resonant technology are achieved, which generally the use of turn-off relief capacitors over the electronic Switching enables (= minimization of switch-off losses), but the undisturbed Relief capacitors can swing around reliably,  which is switching on the electronic switches with zero current and zero voltage (= Minimization of switch-on losses) made possible by known circuit measures, which reduces the heat development of the previous saturation chokes (= better Efficiency), which greatly reduces the reverse currents of the secondary rectifiers, and which reduces the total interference radiation of the inverter.

This object is achieved according to the invention in that in series with the primary winding of the transformer the choke winding of a symmetrical transducer is switched on, which has a separate choke winding and control winding and by means of a Three leg core or by two separate toroidal cores and that the Control winding of the transducer flows through the output current of the inverter current source becomes.

An equivalent solution can be achieved in that on the secondary side of the Inverters a rectifier is used in full bridge circuit, and that in series with the Secondary winding of the transformer is the choke winding of a symmetrical transducer is switched on, each with its own choke winding and control winding and is built up by means of a three-legged core or by two separate ring cores and that the control winding of the transducer from the output current of the inverter current source is flowed through.

An alternative equivalent solution is further achieved in that Secondary side of the inverter, a rectifier is used in the center circuit, and that in series with the secondary winding of the transformer the choke windings symmetrical transducer, which has two identical and parallel choke windings and has a control winding and by means of a three-legged core or two separate ones Toroidal cores is built up, is switched on in such a way that the beginning of the first and the End of the second parallel choke winding at the outer ends of the secondary winding Transformers are connected, and that the end of the first and the beginning of the second  Choke winding with the equivalent connections of the two rectifier diodes be connected, and that the control winding of the transducer from the output current of the Flows through the inverter power source, generally reversing the order of the Circles mentioned components in the same current leads to equivalent function and is also claimed.

A further embodiment of the invention in a primary-side transducer provides that the connection point of transformer and transducer with one free-wheeling diode against each two poles of the DC voltage supply is connected.

Particularly good results with the diode reverse currents of the secondary rectifier and with The interference radiation can be achieved if the turns ratio of the Transductor is designed according to claims 5 and 6.

The invention will now be explained in more detail with reference to drawings. It shows:

Fig. 1 is an essential embodiment of the invention described with primary full-bridge and transducer on the primary side,

Fig. 2 is a resonant circuit in the transformer circuit with conventional half-bridge,

Fig. 3 is a non-resonant transformer in the loop circuit of a conventional type with a primary full-bridge, with Ausschaltentlastungskondensatoren over the switches and additional auxiliary Umschwingkreisen,

Fig. 4 is an improvement of this circuit by the invention with a transducer on the primary side,

Fig. 5 shows an embodiment of the transducer with a three-leg core,

Fig. 6 shows an embodiment of the transducer with two ring cores,

Fig. 7 shows a basic arrangement of transducer at the secondary side and rectifiers in full-bridge circuit,

Fig. 8 shows a basic arrangement of transducer at the secondary side and rectifier in a center tap connection,

Fig. 9 shows a simple practical implementation of this circuit with a transducer which is formed by two ring cores.

Fig. 1 shows the basic arrangement of the inverter power source according to the invention. A DC voltage source 1 feeds the two half bridges with the electronic switches 2 and 3 as well as 4 and 5 . The specific design of these switches with their control circuits is known and should not be discussed. The free-wheeling diodes 19 protect the switches from inverse currents. The half bridges should be controlled with a duty cycle of approx. 50% and the voltages at the center points should swing from one voltage rail to the other in one go if possible. An inverter of this type is usually controlled with a phase shift modulation, so that both half bridges have the same switching frequency. The midpoints of the two half bridges are now connected to one another by a series connection of the transformer 6 , the choke winding of the transducer 7 and an optional capacitor 11 . As a possible embodiment of the output circuit, the diodes 8 are used for rectification and a choke 9 and a capacitor 10 for smoothing. The output current of the inverter current source is guided according to the invention via the control winding of the transducer 7 and automatically controls the transducer so that the throttle effect is minimal at full load and optimal in the lower part-load range. The desired inductance profile of the transducer can be achieved by dimensioning the transducer core and possibly by inserting an additional air gap. The capacitor 11 serves to avoid DC biasing of the transformer 6 and can be omitted if this is prevented by other known measures.

Fig. 2 shows one of the conventional circuits with a primary half-bridge circuit and resonant transformer circuit. The center point of the half-bridge 2 and 3 is connected to the split resonance capacitor 11 via a series connection of the transformer 6 with a choke 12 . The resonance capacitor 11 serves here as a capacitive center and is charged to significant voltages. The courses of current and voltage in this inverter are far from the rectangular shape and lead to an unfavorable use of the electronic switches and the transformer.

Fig. 3 shows a conventional arrangement with the transformer circuit is not a resonant circuit and a primary full-bridge, as is widely performed in a distributed on the market welding machine. Switch-off relief capacitors 13 are provided above the switches and additional auxiliary oscillation circuits formed from the chokes 14 and the capacitors 15 . The diodes 19 serve as free-wheeling diodes. The circuits 14 and 15 are intended to ensure that the switch-off relief capacitors 13 swing around when there is no or a small load and are present here on both half-bridges. In the partial load range, however, the problem arises that the currents of the circuits 14 and 15 overlap with the primary transformer current and the capacitors 13 become currentless. This means that the swinging cannot take place and switches 2 to 5 briefly switch charged capacitors. There are two solutions to this difficult problem. The first is to increase the currents in circles 14 and 15 . However, this makes these parts large and expensive and the switches 2 to 5 must also carry these higher currents. The second solution is in series with the transformer 6 is either primary or secondary, a throttle 16 to switch a saturable reactor or better sixteenth This choke prevents the instantaneous current rise of the transformer current in the moments of commutation of a half bridge, but then steals the transformer a considerable voltage-time area at full load and leads to poorly used components. In addition, the saturation choke 16 usually becomes very hot, requires special cooling and depresses the efficiency.

In the variant of the solution shown here, saturation reactors 17, mostly in the form of ring cores, are additionally located on the secondary side of the transformer 6 in series with the rectifier diodes 8 . These are helpful to make the commutation of the rectifier diodes 8 softer and to keep the diode reverse currents and losses within reasonable limits. Here, too, it applies that these chokes rob 17 valuable voltage time area, become hot and lead to poor utilization of the components.

Fig. 4 shows an equivalent circuit using the features of the invention. The saturation choke 16 from FIG. 3 is removed and the transducer 7 is used in its place. There are some unexpected effects. Several previous problems can be solved with this single measure. First, the transferable voltage time area becomes significantly larger, since the value of the inductor decreases with increasing output current, while the induction value is sufficiently high in the difficult part-load range. Secondly, the introduction of the transducer makes the transformer current very low-harmonic and round, which is very positive for all components and for interference radiation. Thirdly, trapezoidal diode currents now result in the diodes 8 with optimal gradient profiles. Fourthly, if the turns ratio of the transducer 7 is selected as described in claim 6, optimally low and round diode reverse currents are obtained. This leads to high efficiency, low interference radiation and best component utilization. Therefore, the secondary-side saturation chokes 17 from FIG. 3 can now be omitted, the transducer also takes over this function. Fifthly, the measures described only magnetize the core material of the transducer on one side, so that the transducer core remains 2-3 times colder compared to the previous saturation chokes.

The two free-wheeling diodes 18 limit the maximum primary transformer voltage to the value of the voltage source and thus limit the reverse voltage of the secondary rectifiers, but are not absolutely necessary.

Fig. 5 shows the basic structure of the symmetrical transducer with a three-legged core 22 from z. B. ferrite. The choke winding is divided equally between the two outer legs, while the control winding sits on the middle leg. The winding direction and the series connection of the two choke windings must be such that there is no flow through the middle leg.

Fig. 6 shows another possible construction of the symmetrical Transducer with two separate toroidal cores 23rd The control winding is in phase on one core and in phase opposition to the choke winding on the other.

Fig. 7 shows an alternative structure according to claim 2, in which the transducer 7 is now arranged on the secondary side of the transformer 6 . The version shown here applies to use in full bridge rectification using the four diodes 8 . The advantage of the secondary arrangement of the transducer is that there is no safety-relevant isolation of the primary and secondary and that the choke winding of the transducer receives significantly fewer turns. This circuit can also be expanded by the use of relief capacitors and optional auxiliary swinging circuits, as in FIG. 4, so that the electronic switching elements are substantially freed from their on and off switching losses.

FIG. 8 shows a further alternative construction according to claim 3, in which the transducer 7 is also arranged on the secondary side of the transformer 6 . The embodiment shown here applies to use with a rectifier in the center circuit by means of the two diodes 8 . As is known, the advantage of this circuit compared to FIG. 7 lies in the fact that the voltage drop is lost in each case only one diode and therefore higher efficiencies can be achieved. The choke winding of the transducer 7 is divided here into two identical and equivalent paths, which are connected according to claim 3. This circuit can also be expanded by the use of relief capacitors and optional auxiliary swinging circuits, as in FIG. 4, so that the electronic switching elements are substantially freed from their on and off switching losses.

Fig. 9 shows a sketch of how the practical implementation of the transducer according to claim 3 with two separate toroidal cores can look. Fig. 9 shows the secondary circuit of the same circuit as in Fig. 8. In this example, the choke winding and the control winding are each carried out with only one turn. You then only need to run the connecting cables of the components through a toroid. In this example, the simple implementation of the arrangement according to the invention is particularly clear.

The advantages of the invention can be clarified by comparing this arrangement with FIG. 3. There are also two chokes 17 - usually designed as ring cores - in series with the diodes 8 . The throttle value in FIG. 3 is constant in the decisive functional moment, while it is reduced in FIG. 9 as a function of the output current. Second, both chokes 17 are saturated when the current is distributed approximately equally between the two diodes 8 in the free-running time, so that the transformer 6 is thus short-circuited on the secondary side via the two then conductive diodes 8 . For this reason, a primary-side choke 16 is also required in FIG. 3, since the short-circuited transformer 6 immediately draws primary current when the two half-bridges swing around and thus disturb the swinging. This choke 16 is no longer necessary according to the arrangement of FIG. 9. In Fig. 3 the output circuit lacks the full voltage-time area of two saturation chokes, in Fig. 9 only one, which is reduced more and more with increasing current.

Claims (6)

1. Inverter current source, in which the voltage provided by a direct voltage source ( 1 ) is converted by electronic switches into an alternating voltage with frequencies, in particular over the hearing range, in order to feed them to a transformer ( 6 ) and then to rectify them and smooth them if necessary (e.g. with chokes ( 9 ) and capacitors ( 10 )), in which freewheeling diodes ( 19 ) are provided if necessary above the electronic switching elements, four electronic switches ( 2 to 5 ) forming a full-bridge circuit on the primary side and the primary winding of the transformer ( 6 ) is connected in series with an optional capacitor ( 11 ) and / or an optional choke ( 12 ) between the two center points of the half bridges or two electronic switches ( 2 and 3 ) form a symmetrical half bridge circuit, a capacitive center connection is present and the primary winding of the transformer ( 6 ) in series with one optional choke ( 11 ) between the center of the half-bridge ( 2, 3 ) and the capacitive connection, and wherein the primary-side (n) half-bridge (s) swings from one voltage pole to the other in a continuous course (swing) and a duty cycle of 50% (have), characterized in that in series with the primary winding of the transformer ( 6 ) the choke winding of a symmetrical transducer ( 7 ) is switched on, each having an independent choke winding and control winding and by means of a three-legged core ( Fig. 5) or by two separate toroidal cores ( Fig. 6), and that the control winding of the transducer ( 7 ) is flowed through by the output current of the inverter current source ( Fig. 1). 2. Inverter current source, in which the voltage provided by a direct voltage source ( 1 ) is converted by electronic switches into an alternating voltage with frequencies, in particular above the hearing range, in order to feed them to a transformer ( 6 ) and then to rectify them and, if necessary, to smooth them over at if necessary, the electronic switching elements are provided with free-wheeling diodes ( 19 ), four electronic switches ( 2 to 5 ) forming a full-bridge circuit on the primary side and the primary winding of the transformer ( 6 ) in series with an optional capacitor ( 11 ) and / or an optional choke ( 12 ) is connected between the two center points of the half-bridges or two electronic switches ( 2 and 3 ) form a symmetrical half-bridge circuit, a capacitive center connection is present and the primary winding of the transformer ( 6 ) in series with an optional choke ( 11 ) between the center the half-bridge ( 2, 3 ) and the capacitive connection, and wherein the primary-side half-bridge (s) swings from one voltage pole to the other in a steady course and has a duty cycle of 50%, thereby characterized in that a rectifier ( 8 ) in full bridge circuit is present on the secondary side of the inverter and that in addition in the series connection of the secondary winding of the transformer ( 6 ) and the full bridge rectifier the choke winding of a symmetrical transducer ( 7 ) is switched on, each via an independent Choke winding and control winding and is constructed by means of a three-legged core ( Fig. 5) or by two separate toroidal cores ( Fig. 6), and that the control winding of the transducer is flowed through by the output current of the inverter current source ( Fig. 7). 3. Inverter current source, in which the voltage provided by a direct voltage source ( 1 ) is converted by electronic switches into an alternating voltage with frequencies, in particular above the audible range, in order to feed them to a transformer ( 6 ) and then to rectify them and, if necessary, to smooth them over at if necessary, the electronic switching elements are provided with free-wheeling diodes ( 19 ), four electronic switches ( 2 to 5 ) forming a full bridge circuit on the primary side, and the primary winding of the transformer ( 6 ) in series with an optional capacitor ( 11 ) and / or an optional choke ( 12 ) is connected between the two centers of the half-bridges or two electronic switches ( 2 and 3 ) form a symmetrical half-bridge circuit, a capacitive center connection is present and the primary winding of the transformer ( 6 ) in series with an optional choke ( 11 ) between the Focus the half-bridge ( 2, 3 ) and the capacitive connection, and wherein the primary-side half-bridge (s) swings from one voltage pole to the other in a steady course and has a duty cycle of 50%, thereby characterized in that a rectifier ( 8 ) is present in the center circuit on the secondary side of the inverter, and that in series with the secondary winding of the transformer ( 6 ) and the rectifier ( 8 ), the choke windings of a symmetrical transducer ( 7 ), which has two identical and has parallel choke windings and a control winding and is built up by means of a three-legged core ( FIG. 5) or by two separate toroidal cores ( FIGS. 6 and 9), in principle in such a way that the beginning of the first and the end of the second parallel choke winding are connected to the outer ends of the secondary winding of the transformer ( 6 ), and that the end of the first and the beginning de r second choke winding are connected to the equivalent connections of the two rectifiers ( 8 ), the other two connections of the rectifiers ( 8 ) being connected to one another, and that the control winding of the transducer is traversed by the output current of the inverter current source ( Fig. 8). 4. Inverter current source according to claim 1, characterized in that the connection point of the transformer ( 6 ) and transducer ( 7 ), each with a free-wheeling diode ( 18 ) against the two poles of the DC voltage source ( 1 ) is connected ( Fig. 4). 5. Inverter current source according to claim 1, characterized in that the transducer ( 7 ) is designed so that the turns ratio of the choke winding to the control winding has approximately the value of the transformation ratio of the transformer ( 6 ) from the primary winding to the secondary winding and is valid for each of the two cores in the case of a transducer structure with two separate toroidal cores ( FIG. 6), or twice the value in the case of the transducer structure from a three-legged core ( FIG. 5) in relation to the entire choke winding of the core. 6. Inverter current source according to claim 2 or 3, characterized in that the transducer ( 7 ) is designed so that the turns ratio of the choke winding to the control winding has approximately the value one, and is valid for each of the two cores in a transducer structure with two separate toroidal cores ( Fig. 6 and 9), or double the transducer structure from a three-legged core ( Fig. 5) based on the entire choke winding of the core.